Method for levelling sheet stock



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R. G- BROWNST METHOD FOR LEVELLING SH EIN 3,459,027

EET STOCK Filed Sept. 28, 1967 \NCEPHON OF STRNN HRQDEBHNG mvsmon F4 wow6. Bmwsrsm PERCENTAGE $TRNN STRESS-STRNN CURVE FOR M\\ D STEEL ATTORNEYSUnited States Patent 3,459,027 METHOD FOR LEVELLING SHEET STOCK RaymondG. Hrownstein, 300 Fountain Ave, Ellwood City, Pa. 16117 Filed Sept. 28,1967, Ser. No. 671,265 Int. Cl. BZIb 1/38; B2111 1/02, 3/02 U.S. Cl.72366 Claims ABSTRACT OF THE DISCLOSURE This invention relates to thetreatment of metal sheet stock in order to prepare it for furthermanufacturing operations.

Metal sheet stock to be used for stamping or drawing is rarely suitablefor its ultimate use without further treatment. Metal plate afterrolling, or metal strip after uncoiling, is passed through a leveller inorder to flatten it preparatory to moving on to other operations. Theleveller in use today normally has anywhere from nine to twenty-threestaggered rollers which cause the material to pass through a series ofreversing bends thereby producing a straight sheet. Since the materialis not uniformly flat those areas that are flat are bent within theelastic limit, and the areas that are not flat are bent beyond theelastic limit. The commercially flat product results from thiscombination of bending and springing back repeated a sufficient numberof times. The size of the rollers, number of rollers, and roller spacingare determined by the type and dimensions of the material being worked,which usually is no more than 1 /2 thick. When metal sheet stock islevelled on such an apparatus, plastic stress is set up in the outerone-third of the material from the neutral axis. In order to perform therequired operations on a material being treated with this commonly usedapparatus, the operator must make many adjustments, the most importantof which is roller spacing. The required results in the product areachieved by passing the sheet stock through the apparatus several times,or passing it through several similar machines which represent asignificant investment in terms of equipment and labor and which take upan undue amount of floor space.

When thin sheet stock is passed through such conventional apparatus,bridles must be located at the entry and exit ends of the apparatus tomaintain proper tension in the material. This, of course, means thatthere is additional equipment which must be separately installed,thereby further increasing operating costs on such conventionalapparatus.

Accordingly, it is an object of this invention to provide a method ofstraightening metal sheet stock which overcomes the aforementioned andother such disadvantages. It is a further object of this invention toprovide a method of straightening metal sheet stock which is relativelyfast and easy to perform.

An additional object of this invention is to provide a method ofstraightening metal sheet stock consistent with the foregoing objectswhich eliminates complicated equipment, is simple, and provides improvedresults in a single pass through the appropriate apparatus.

These and other objects of this invention will become apparent byreference to the following description and the drawings wherein:

FIGURE 1 is a diagrammatic side elevational view of an apparatus whichcan be utilized to perform the method of this invention;

FIGURE 2 is an end view of the apparatus of FIG- URE 1 with someportions omitted for clarity; and

FIGURE 3 is a stress-strain curve for mild steel to be treated inaccordance with the present invention.

I have found that metal sheet stock, particularly steel, develops aso-called hinge when subjected to forces that produce a plastic stress.Such forces may be set up by compressing or bending the stock, or by acombination of compression and bending. Compressing the stock betweenrollers with a suitable load sets up a definite volume under plasticstress and elongates the fibers of the stock, in the plastic volume, inthe direction of travel. This is best accomplished by using rollers ofdifferent sizes. The compression gives the fibers a certain flatness atthe point of contact, or hinge. By bending or tensing the stock as itemerges from the rolls, to a particular degree, the fibers are orientedin a definite direction or plane of travel and all fibers follow in thissame plane to produce flat stock.

The degree of compression, and the angle at which the stock is bent, aredependent on the stock material itself and are determined by the plasticlimit of the material. The method of this invention is based upon thisobservation and upon the fact that the plastic stress applied to thesheet stock is in the full thickness of the same.

Metallic materials, and particularly steel, are characterized by thefact that plastic limit or the maximum plastic stress that can beapplied is reached before strain hardening begins. The total plasticstress applied by compressing the material between the rollers and bybending the material as it emerges from the rollers must not exceed itsplastic limit. Thus, it may be seen that the load applied to the rollersand the angle at which the material is bent will be regulated accordingto this characteristic of the material.

Turning now to FIGURE 1 of the drawings, the metal sheet stock 10,preferably formed of steel, is guided into the apparatus by the entryroll 12 and between the feed roll 14 and the pressure roll 16 withcompression being applied at 18. Platic stress results at point 18 whichis termed the hinge causing the crystals, or fibers of the stock 10 toelongate in the direction of travel. As the stock 10 emerges frombetween the feed roll and the pressure roll, the exit roll 20 bends thestock angularly downward and out of its feeding plane, the degree ofbend being exaggerated in the drawing for purposes of illustration. Ascan be seen, the feed roll 14 is of greater diameter than the pressureroll 16, and in the preferred embodiment, the ratio of the diameters ofthe feed roll to the pressure roll is approximately 2:1. Ideally, a rollwould bear on a flat surface to produce the desired plastic stress.Since such a construction would be impractical, the ideal situation mustbe approximated. This is done by using a diameter ratio as large aspossible. Practical considerations such as cost, size, driverequirements etc., however, force a compromise, which is reflected inthe 2:1 ratio as most practical for most applications, but not as alimiting ratio. The angle at which the stock is bent is regulated by thesetting of the exit roll 20 which is adjusted by known means, as are theentry, feed and pressure rolls 12, 14 and 16.

In FIGURE 2, the apparatus is shown in an end view incorporating anadjusting means, generally designated by the numeral 24, at each end ofpressure roll 16. The adjusting means 24 includes a pressuretransmitting member 26 into which the end of the roll 16 is journaled.Adjusting screw 28 threadedly engages cross-beam portion 30 of the mainsupporting frame generally designated 32 and is secured by lock nut 34.Adjusting screw 28 raises or lowers spring seat 36, thereby applyingpressure to spring 38 which bears on pressure transmitting member 26.

By properly adjusting the screws 28, the spring seats 36 can beselectively raised or lowered and the pressure placed on the roll 16 bysprings 38 easily adjusted. Suitable means (not shown) are provided forOpening rolls 14 and 16 for easy material entry without disturbing thepressure setting.

While a preferred embodiment is described for loading the adjustingmeans 24 it is clear that any suitable means such as fluid cylinders ortorque devices could be substituted for the spring loaded adjustingmeans. Whatever means is used must insure uniform roll force across theface of the pressure roll.

This method may be used with stock of any thickness t and is onlylimited in this respect by practical consideration since there is nottheoretical maximum thickness of material which may be straightened.When using this method with thin metal sheet stock, it is necessary toutilize entry and exit bridles to maintain sufficient tension in thematerial. The bridles may be mounted, unlike prior art equipment andmethods, in the same housing as the entry, pressure, feed, and exitrolls and are preferably located as close to the entry and exit rollsrespectively as possible.

A specific embodiment of this invention, not to be considered undulylimiting, is described in the following example:

Example A semi-circular mild steel bar 2" wide and /2 thick was passedonce through a leveller with 3" diameter entry and exit rolls, a 4"diameter pressure roll and an 8" diameter feed roll. The rolls were 9"long.

By reference to FIGURE 3 it can be seen that the plastic range for themild steel ranges from about 0.1 to about 1.5% strain, therefore theallowable plastic forces applied to this material must not exceed 1.5%.

The load applied to the pressure roller, and thence to the steel bar asit passed through the rolls, was calculated using the following formula:

where:

S =Maximum compressive stress=33,000 p.s.i. P=Load applied per linearinch E=Modulus of elasticity=30 l0 d=Diameter of pressure roll=4 inchesM (.59l) E :417 pounds per linear inch and for 2 inch width P=834 poundsThe entry roll was set for a horizontal feed and the pressure roll wasset to apply a force of 834 pounds on the 2 inch wide bar. The exit rollwas set to provide a bend in the bar at the hinge corresponding to /z%additional fiber elongation. The total strain was Within 1 /2 Thelevelled bar, when measured on a flat guage surface, was perfectly fiat.

The apparatus used for this example could level a bar up to about 3" inthickness, being limited only by the size of the particular machine.

It will be readily understood that the method of this invention need notbe limited to any particular material but is applicable to all types ofsteel, aluminum and any other metal which requires levelling at anystage of its manufacture. The amount of compressive force and the degreeof bending are dependent on the material being levelled and can beeasily determined by reference to standard data.

It is apparent that the method of this invention has been described inaccordance with the foregoing objects.

What is claimed is:

1. A method of straightening metal sheet stock comprising the steps offeeding the stock between a pair of parallel straightening rollers whichapply pressure to the stock thereby setting up plastic stress in thestock and elongating the fibers in the stock in the direction of travelof the stock, and then diverting the stock as it leaves the rollers atan angle with respect to the plane of the stock as it passes the rollersto apply additional plastic stress to the stock and to orient theelongate fibers in the stock in the direction of travel, the totalplastic stress applied to the stock being in the full thickness of thestock and within the plastic limit of the stock.

2. The method of claim 1, wherein one of the pair of rollers is greaterin diameter than the other.

3. The method of claim 2, wherein one of the pair of rollers is twicethe diameter of the other.

4. The method of claim 2, wherein the stock is diverted in a directionaway from the smaller of the two rollers.

5. The method of claim 1, wherein the stock is passed horizontallythrough the pair of parallel straightening rollers and then diverteddownwardly as it passes the rollers.

6. The method of claim 5, wherein the parallel straightening rollersconsist of an upper pressure roller and a lower feed roller, said feedroller having twice the diameter of said pressure roller.

7. The method of claim 5, wherein the stock is diverted by means of anexit roller.

8. The method of claim 1, wherein the stock comprises steel and thetotal plastic stress is within 1 /2 percent strain.

9. The method of claim 1, wherein the stock is up to about 3 inches inthickness.

10. A method for straightening metal sheet stock comprising the steps ofhorizontally passing the stock between a pair of parallel straighteningrollers which apply pressure to the stock thereby setting up plasticstress in the stock and elongating the fibers in the stock in thedirection of travel of the stock, said parallel straightening rollersconsisting of an upper pressure roller and a lower feed roller, saidfeed roller having twice the diameter of said pressure roller; and thendiverting the stock downwardly as it passes said parallel straighteningrollers by means of an exit roller, thereby applying additional plasticstress to the stock and orienting the elongate fibers in the stock inthe direction of travel of the stock, the total plastic stress appliedto the stock being in the full thickness of the stock and within theplastic limit of the stock.

References Cited UNITED STATES PATENTS 874,692 12/1907 Lindstrand 72l60X 2,190,986 2/1940 Hudson 72l60 X 2,301,681 11/1942 Cameron 72l603,094,442 6/1963 Perry 148-l2 MILTON S. MEHR, Primary Examiner US. Cl.X.R.

